This invention relates to a process and composition for use in photographic materials containing hydroquinones. The process and composition of this invention are primarily intended for use in diffusion transfer films, which are usually referred to as "self-developing" or "instant" films.
The term "hydroquinone" is used herein generically to refer to any aromatic system in which a single phenyl ring bears two hydroxyl groups in positions para to one another. Thus, the term as used herein includes not only derivatives of hydroquinone itself in which the phenyl ring is substituted, for example 2-phenyl-5-methylhydroquinone, but also compounds in which the phenyl ring bearing the hydroxyl groups is fused to one or more other aromatic rings, for example 1,4-dihydroxynaphthalene.
Hydroquinones have found widespread use as developers in photographic systems of both the conventional (wet-processed) and instant types; see, for example, Lee, W. E. and Brown, E. R., in Chapter 11 of James, T. H. (ed.), The theory of the photographic process, Macmillan, New York (1977). Many instant films (such as those described in, for example, Walworth, V. K. and Mervis, S. H., Instant photography and related reprographic processes, in Sturge, J., Walworth, V. K., and Shepp, A. (eds.), Imaging materials and processes--Neblette's eighth edition, Van Nostrand Reinhold, New York, NY (1989), and references cited therein, especially U.S. Pat. No. 2,983,606 to Rogers and U.S. Pat. No. 4,740,448 to Kliem) comprise a photosensitive element, an image-receiving element and a device (usually a disruptible pod) for contacting the photosensitive element with an alkaline developing composition. The photosensitive element has one or more silver halide emulsion layers each of which has associated therewith a dye developer, that is to say a compound which contains both a silver halide developing moiety and the chromophore of a dye. Upon exposure of the photosensitive element and contact of the alkaline developing composition therewith, in unexposed regions the dye developer diffuses to the image-receiving element. However, in exposed regions, the dye developer is oxidized and immobilized, so that no transfer of dye developer to the image-receiving element takes place. Thus, a positive image is formed on the image-receiving element.
While the dye developer may itself develop exposed silver halide, in practice the dye developer is used in conjunction with a colorless developing agent, sometimes referred to as an "auxiliary developer", "messenger developer" or "electron transfer agent". The auxiliary developer itself develops the exposed silver halide in exposed regions, and the oxidized auxiliary developer thus produced participates in a redox reaction with the dye developer, thereby oxidizing and immobilizing the dye developer. The auxiliary developer is usually a hydroquinone.
The photosensitive elements of instant films may also make use of processes in which a diffusible image dye is released from an immobile precursor by silver-initiated cleavage of certain sulfur-nitrogen containing compounds, such as thiazolidines. As described, for example, in the aforementioned U.S. Pat. No. 4,740,448, such thiazolidines are used in conjunction with a colorless developing agent or "primary developer", which is usually a hydroquinone.
Thus, the photosensitive elements of most instant films contain at least one hydroquinone, and color instant films may contain more than one hydroquinone. For example, the photosensitive elements described in Examples 2 and 3 of the aforementioned U.S. Pat. No. 4,740,448 each contain two separate layers each containing 4'-methylphenylhydroquinone (MPHQ) and a third layer containing 2-phenyl-5-t-butylhydroquinone.
Unfortunately, hydroquinones tend to be highly mobile in the polymeric media used in the photosensitive elements of instant films, especially at highly alkaline pH, and the mobility of the hydroquinones can cause various problems. Firstly, during development the hydroquinones tend to transfer to the image-receiving element with the dyes. Although the presence of hydroquinone in the image-receiving layer does not affect image formation, upon extended storage the hydroquinone tends to be oxidized by atmospheric oxygen to the corresponding quinone, which may produce an undesirable yellow or straw color in white regions of the image. Secondly, in a color film containing a plurality of hydroquinone-containing layers, a hydroquinone intended for use with one dye may diffuse, either during storage before exposure or during development, into a layer containing a hydroquinone intended for use with a different dye. The presence of the "wrong" hydroquinone in a layer may cause color mixing, as discussed for example in U.S. Pat. No. 4,293,641 to Takahashi et al. These diffusion problems are exacerbated by the need to keep the individual layers of an instant film very thin (of the order of 1 .mu.m) in order to provide a high resolution image within a reasonable development time.
The incorporation of hydroquinones into photosensitive elements of instant film units by conventional coating procedures also presents difficulties. Some hydroquinones cannot be dispersed in water, so that they must be coated from non-aqueous media, which present environmental and waste-disposal problems and costs. For example, in the aforementioned U.S. Pat. No. 4,740,448 t-butylhydroquinone is coated from a solution in diethyldodecanamide. Even where the hydroquinone can be coated from an aqueous dispersion, the hydroquinone is frequently susceptible to atmospheric oxidation during coating, and the presence of quinone in the photosensitive element not only effectively wastes part of the hydroquinone but may also lead to color distortion problems caused by the quinone oxidizing and immobilizing dye developer, even in unexposed areas of the photosensitive element.
It is known that hydroquinones will form hydrogen-bonded complexes with certain nitrogenous organic compounds, and attempts have been made to use such complexes in imaging systems. For example, U.S. Pat. No. 4,097,288 to Lawton, describes a heat sensitive recording composition containing normally colorless lactones or spiropyran compounds in combination with hydrogen bonded molecular complexes of phenolic compounds with mines or amides, these complexes having a dissociation temperature ranging from 50.degree. to 220.degree. C. The composition is stated to be less sensitive to pressure and less susceptible to background staining, image flooding, moisture sensitivity, odor, railroading and burnout problems as compared with compositions in which phenolic compounds are not complexed. Among the specific complexes disclosed are complexes of hydroquinone with acetamide and formamide.
The aforementioned U.S. Pat. No. 4,293,641 describes a photographic light-sensitive material comprising a support having at least two silver halide photographic emulsion layers capable of forming a silver image upon treatment with an alkaline processing solution in the presence of a developing agent for silver halide after exposure, and an interlayer positioned between the emulsion layers, this interlayer containing a complex formed from a mixture of hydroquinone derivatives having a solidifying point of 100.degree. C. or less, and which are different compounds from the developing agent for silver halide used in the treatment of the material, and a homopolymer or copolymer containing pendant lactam rings. This interlayer is stated to substantially prevent color mixing. However, this proposed solution to the color mixing problem requires the provision of an additional layer in the photosensitive element, which layer must include a hydroquinone different from that used to develop the silver halide emulsion layers, and also requires the preparation of the polymer for the interlayer. This patent does not suggest any way of dealing with the problem of discoloration of the image caused by diffusion of hydroquinone to the image-receiving element.
It has now been found that complexes of hydroquinones with certain simple, monomeric dimides can be used in place of the hydroquinones themselves in instant films to reduce or overcome some of the problems associated with the use of hydroquinones in such films. In addition, the provision of these diamides at locations within the films where the diamides can form complexes with the diamides during or after development reduces or overcomes other problems associated with the use of hydroquinones in such films.